California: Kreyenhagen siltstone yields oil on test

By OGJ editors
– A brittle, low-permeability, fractured siltstone in the Eocene Kreyenhagen formation has tested at the rate of 24 b/d of oil with a GOR of 368 scf/bbl and a load fluid recovery of 39 b/d at a well in Kings County, Calif.

Zodiac Exploration Inc., Calgary, decided to test the Kreyenhagen at the 4-9 vertical test well on the Jaguar prospect in Kings County just east of Kettlemen North Dome oil field based on encouraging core and petrophysical log evaluation.

The 30-ft Kreyenhagen interval was perforated and stimulated with a water-based fluid and a volume of 195 bbl of 29° gravity oil, and 58% of the load fluid was recovered in 9 days.

Kreyenhagen being a secondary target, the company did not wish to conduct an extended test, which would require the continuous unloading of the wellbore, as it would have further delayed tests of the primary targets. The company is moving uphole to complete and evaluate the primary targeted zones in the Vaqueros and Whepley formations. Work is expected to continue through August 2011.

By establishing oil productivity from 30 ft of a total 150 ft of equivalent Kreyenhagen siltstone in this well, Zodiac said, the company believes it has identified a potentially important and significant new play type. These test results indicate that even with a limited stimulation, these low permeability reservoirs in the Kreyenhagen will flow at rates that are typical of early nonoptimized well completions in other more well known resource plays in the US.

The Kreyenhagen formation had produced more than 1 million bbl of oil from legacy vertical wells in the field just west of the 4-9 well, but it was not known whether productivity could be demonstrated from this formation on the company’s lands. These siltstones represent potential reservoirs in the Kreyenhagen formation.

Zodiac added, “In addition to the thickness observed in the siltstones on the 4-9 well they have also been observed to be approximately 500 ft thick on an abandoned well bore located on company lands approximately 10 miles south of the 4-9 well. Further evaluation will be required in subsequent wells to determine optimal completion strategies and economic thresholds.”

The range of thickness of 150 to 500 ft for the siltstones in the Kreyenhagen is not likely to be present across 100% of the company’s land holdings and therefore may not be prospective on all of its lands. The company holds 87,000 net acres in the San Joaquin basin.

The completion program for the 4-9 well has been expanded from the original budget of $2 million to $8 million in order to more effectively test several intervals.

Zodiac plans to spud the 1-10 well, its first horizontal well, in mid to late June 2011 (OGJ Online, May 20, 2011). The horizontal target has not yet been finalized but is expected to be in the Vaqueros formation. Given the extended time to drill and test the 4-9 well, the company now expects to only drill and complete the 4-9 well and be in the completion phase in the 1-10 well by Sept. 30, 2011, the end of its fiscal year.

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